This invention relates to novel large area sources of ions and methods for producing them.
Extraction of a single ion beam from liquid metals is a common procedure. However, up to this point liquids have not been used to produce large-area ion beams.
Liquid-metal ion sources usually consist of a capillary filled with a liquid metal or a small radius needle that is wetted with a liquid metal. M. D. Gabovich, Sov. Phys. Usp. 26, 447 (1983); U.S. Pat. No. 4,318,029; U.S. Pat No. 4,318,030; and Hendricks, et al., AIAA, Vol. 18, 1973, pp. 295-300. The liquid metal serves as an anode to which an extracting voltage is applied. Ion emission from a sharp edge wetted liquid metal (edge emitter) has also been reported. R. Clampitt and D. K. Jefferies, LEIB I, Salford, Inst. Phys. Conf. Ser. 38, Chap. 1 (1978). The liquid metal deforms under the competing effects of surface tension and electrostatic stress. When the applied field is high enough, the liquid metal at the tip of a needle or capillary is drawn up into a cusp. G. Benassayag, P. Sudraud and B. Jouffrey, Ultramicroscopy 16, 1 (1985). Cusps also form along the razor edge of the edge emitter. Clampitt et al, supra. The electric field in the vicinity of the cusps is greatly enhanced and field evaporation of ions occurs.
A similar ion source is disclosed in U.S. Pat. No. 4,328,667. This system involves the field-emission of ions from a liquid through a very narrow slit. See also, Bartoli et al, J. Phys. D: Appl. Phys. 17 (1984), pp. 2473-2483. Like the above-mentioned devices, the devices of these references are essentially unidimensional. Two-dimensionality is attempted by simple stacking of the one dimensional devices. However, for many applications, the resultant current density is much too low, e.g., for fusion applications, e.g., as discussed in U.S. Pat. No. 3,533,910, with respect to lithium ion sources. Furthermore, of course, these prior art devices are not true two dimensional devices, i.e., large surface area devices.
Heretofore, there has been no suggestion of whether or how true two dimensional ion generation from suitable liquid sources may be achievable in practice. Such large-area sources would satisfy the still existing need, e.g., for high density, preferably tunable, ion current devices. For special applications, e.g., for the light ion-beam driver needed for inertial confinement fusion, whether such devices, even if they were available, would successfully provide the required current densities, (e.g., on the order 5 kA/cm.sup.2) in the required very fast growth times (e.g., on the order of 1.0 ns), is unpredictable.